Many of the current motor vehicles are equipped with a smart entry system that allows a vehicle operator to unlock the door and start the engine simply by carrying a smart key (electronic key) for enhanced convenience and security. For instance, upon detecting that a vehicle operator has held a door handle by using a capacitive sensor or the like, the main body (onboard unit) of a smart entry system communicates with a smart key carried by the vehicle operator via an antenna incorporated in the door handle, and unlocks the door by comparing an ID code transmitted from the smart key to an ID code stored in ROM of the main body. Typically, a smart entry system includes an antenna incorporated in a door handle or a trunk lid so that the onboard unit may communicate with an electronic key via such an antenna.
A motor vehicle incorporated with a smart entry system typically uses a hollow door handle including a handle main body and an outer cover to receive a capacitive sensor and an antenna therein. The handle main body and outer cover are typically made by injection molding plastics for the efficiency in mass production and reduction in weight and cost. The texture of a door handle has a large impact on the aesthetic appearance thereof, and a door handle having a metallic appearance on its surface is preferred. Normally, when a metallic film is formed on the surface of a door handle by plating so as to produce a metallic appearance, it is necessary that the metallic film has a thickness in the range of 50 μm and 75 μm. However, when such a thick metallic film is formed, it means that the antenna is covered by a conductor and a significant reduction in the output of radio-magnetic radiation is inevitable. To overcome this problem, it was proposed to coat the outer cover with a paint containing metallic particles (gloss material) so as to produce the appearance of a metal-plated surface (see Japanese patent laid open publication No. 2005-113475). According to this method, because there are gaps (discontinuous parts) between the metallic particles, the loss in the antenna output can be controlled at will in substantially the same manner as when pure plastic material is used or tinted in the same color as the vehicle body.
According to the door handle disclosed in Japanese patent laid open publication No. 2005-113475, as it is difficult to rigorously control the thickness of the coating and metallic particles tend to be distributed unevenly in the coating, an uneven distribution of discontinuous parts is inevitable. As a result, the range of communication with the electronic key varies depending on the position of the electronic key relative to the door handle, and this prevents a stable communication. As the coating on the door handle of Japanese patent laid open publication No. 2005-113475 is no more than a coat of paint containing metallic particles, it is unable to produce a metallic appearance similar to that of a metallic plating.